In traditional barrier layer, polycrystalline dielectrics, electrons are the mobile species. Use of electrons as the mobile species enables these dielectrics to achieve relatively high frequency response. The operating voltage of these dielectrics, however, is limited by electric field drop across grain boundaries as well as by tunneling of electrons across grain boundaries. This, in turn, limits the capacitive energy density that can be achieved.
Typical barrier layer dielectrics provide effective relative permittivities of about 20,000 to 100,000. The energy storage capacity of these dielectrics however, is limited by electron tunneling at the grain boundaries under high electric fields. Also, typical barrier layer dielectrics are only able to withstand low voltages of about 3 Volts.
Commercial barrier layer dielectrics are based on semiconducting dielectric grains that have resistive grain boundaries and display a heterogeneous distribution of resistivity. These dielectrics utilize a space charge under electric field bias to develop a polarizable dielectric that has segregated charge distributions. The dielectric grains in commercial, polycrystalline barrier dielectrics have high conductivities and typically are n-type. The grain boundaries in these dielectrics, however, are more resistive than the grains and have a double Schottky barrier potential. This limits DC conduction through the polycrystalline dielectric until tunneling occurs across the grain boundaries under high electric field bias.
The art has attempted to reduce the probability of electron tunneling by addition of a more resistive phase such as silica or alumina at the grain boundaries of the dielectric. Breakdown, however, nevertheless is controlled by electronic conduction across grain boundaries.
A need therefore exists for new materials that address these deficiencies.
A further need exists for devices that may employ these new materials such as in high energy density storage applications.